Impact tool



J. STURROCK IMPACT TOOL Feb. 28, 1961 2 Sheets-Sheet 1 Filed 001;. 31, 1956 INVENTOR. JflMES STUF/QOCK Feb. 28, 1961 J. STURROCK 2,973,071

IMPACT TOOL Filed Oct. 31, 1956 2 Sheets-Sheet 2 IN VEN TOR. fin/5 \STUPPOCK IMPACT TOOL cames Stnrroclr, Orwell, Ohio, assignor, by mesne assignments, to Master Power Corporation, Bedford, Ohio, a corporation of Maryland Filed Oct. 31, 1956, Ser. No. 619,510

9 Claims. (Cl. 19230.5)

This invention relates to portable power operated, impact wrenches and similar tools for driving bolts, nuts, screws and the like or for applying an impact rotational torque to other objects.

Tools of this character usually include a motor as a prime mover, a rotatable hammer driven by such motor, and a rotatable work shaft including an anvil member adapted to be struck by the hammer for imparting a high torque to the output shaft. The hammer is repeatedly engageable with and disengageable from the anvil member to permit the motor to rotate the hammer member freely for imparting angular momentum thereto, and to permit the hammer to strike the anvil and impart the momentum of the hammer member to the anvil and work shaft. Disengagement again occurs after the momentum of the hammer has been delivered to the anvil, thereby again permitting free rotation of the hammer assembly for again building up its angular momentum. For practical utility, such tools must also be operable in either direction, for either tightening down or releasing nuts and the like. In tools having two opposite sets of impacting surfaces on the hammer and anvil, the hammer can accelerate through only half a revolution between blows, and in tools having one set of impacting surfaces, the hammer can accelerate through only one revolution-between blows.

In an impact wrench the force of the blow which can be delivered to the Work shaft by the tool is proportional to the mass of the hammer and the square of its velocity. The force of the blow does not react on the operator, so that a blow can be delivered imparting a much higher torque to the work than could be resisted by the operator holding the tool, who must resist only a reaction force equal to the accelerating force applied to the hammer between successive blows. Similarly, the size and weight of the motor may be relatively small compared to the torque delivered by the successive impacts.

The principal object of this invention is to increase the torque than can be delivered to the work in a given number of impact blows, with an impact wrench of a given size, weight, and motor torque reaction, without proportionately increasing the elapsed time between successive blows; or, conversely to reduce the size, weight, cost, and torque reaction of a tool for delivering impact blows of a given torque value; by accelerating the hammer through an angular extent greater than the angle from one impacting position to the next, and particularly through more than one revolution, so asto increase the momentum of each blow with the square of the increase in elapsed time between blows.

Other objects are to attain such increased hammer momentum in either direction of rotation, so that the tool may be used either for tightening or loosening nuts and the like; and to provide a simple, efficient and durable device for preventing impacting until the hammer has been accelerated through more than one revolution, by latching the hammer and releasing the latch by cam means effective after more than one complete relative rotation of the hammer and anvil.

In the illustrated embodiment the invention is applied to an imp-act wrench in which an impact pin is carried by the hammer and alternately projected into and retracted out of the path of a cooperating abutment surface on the anvil by means of air under pressure controlled by a valve responsive to centrifugal force of the type disclosed and claimed in the patent to Maurer No. 2,693,867, issued November 9, 1954. It is to be understood, however, that the invention is applicable to other types of impact wrenches and, in its broader aspects, is not limited to the type of mechanism for effecting engagement and disengagement of the clutch.

In the accompanying drawings which illustrate a preferred embodiment of the invention:

Fig. 1 is a partial central longitudinal section through a rotary impact tool embodying my invention;

Fig. 2 is a vertical section taken on the line 22 of Fig. 1 illustrating the cam and latch mechanism;

Fig. 3 is an enlarged fragmentary view of the latch mechanism and associated parts showing the hammer pin in striking position and the latch disengaged from the hammer pin notch;

Fig. 4 is a fragmentary view taken on the line 44 of Fig. 3, looking in the direction of the arrows;

Fig. 5 is a fragmentary, sectional view taken on the line 5-5 of Fig. 3, showing the latch spring; and

Fig. 6 is a view corresponding to Fig. 3 showing the parts immediately after latch disengagement.

In the drawings the numeral 10 refers generally to the impact wrench tool, mounted in an elongated housing comprising an integral handle and motor housing section 11 and a separate housing section 12 containing or mounting parts of the device driven by the motor, the two housing sections 16 and 11 being suitably flanged and secured together in any convenient manner.

A fluid motor 13, partially illustrated in Fig. 1, preferably is of the reversible type and includes reciprocable blades 14- mounted in a rotor 15 suitably mounted on a hollow motor shaft 16. The rotor 15 is eccentrically mounted in a rotor chamber 17. The motor 13 and the compressed air supply line leading to the motor may for the most part be of conventional design known in the art, and are therefore not described in detail herein. Compressed air is supplied to the motor through a coupling 18 leading into the handle portion of the housing 11 and to a main control valve provided with a control trigger 19 from which suitable air conduits, not shown, lead to the motor. The fluid motor 13 is adapted to receive air under pressure entering the rotor chamber 17 between adjacent pairs of blades 14 which moves the blades about the motor axis in a manner to permit the expansion of the air as it travels toward an exhaust port 20 from where it passes out through exhaust port 20a in the housing 11.

The hollow air motor shaft 16 is splined to a plate 21 which has a conical friction surface 21a on the outside of the plate pressed into a conical surface in the housing of the hammer assembly by spring 22 and retaining ring 23. A ball bearing 24 mounted in front end plate 25 is provided for the motor shaft 16, while a pin 25:: secures the wall of the rotor chamber 17 to the front end plate 25. The central bore through the shaft 16 is open at its rear end to the supply of high pressure air admitted to the motor through the coupling 18 and the con trol valve operated by the trigger 19, so that whenever the motor is being operated high pressure air is present within the shaft 16 for operating the clutch.

An output or work shaft 26, journaled in a bushing 27 suitably mounted in the forward end of the housing 12,

is provided at its outer end with a suitable work driving tip 28. The bushing 27 is provided with a sealing ring 27a and is sufiiciently long to retain the work shaft 26 firmly in alignment with the axis of the rotor and to permit a clutch assembly to be supported solely by and between the work shaft 26 and the hollow rotor shaft 16, as hereinafter described. A radial projection from the Work shaft 26 near its rearward end provides an anvil 29 which is formed with a flat rearward surface 61 and is shaped on opposite sides to provide identical impact surfaces 39 against which an impact pin may strike to drive the output shaft 26 in either direction about its axis for turning work connected to the work driving tip 23. 1

A hollow hammer member 31 mounted in the housing 12 and journalied on the rearward end of output shaft 26 is adapted to be rotated in the housing 12. The rearward end of the hammer 31 is centered and driven by the conical friction surface 21a. An impact pin 32 is mounted for longitudinal sliding movement in a bore through the hammer member 31 parallel to its axis and spaced radially outwardly therefrom. Impact pin 32 is adapted to be projected axially into the path of the anvil 23 for driving it in either direction about its axis, as determined by the direction of rotation of the motor. The pin 32 is also adapted to be withdrawn to permit acceleration of the hammer member 31 between impact blows.

The axial movement of the hammer pin 32 is controlled by a piston 33 slidable in the central bore of the hammer member 31 and provided with a radially disposed boss 34 projecting through a radial slot into the hammer in 32 which looks the piston 33 to the hammer pin 32 so that they reciprocate in the hammer member 31 as a unit, and prevents relative rotation of the hammer 31 and piston 33. A valve 35, slidably disposed in a radial bore 34a extending through the piston 33 and the boss 34, is provided at one end with an enlargement or weighted portion 36. Upon rotation of the motor shaft 16 centrifugal force tends to move the valve 35 to its outward position as illustrated in full lines in Fig. 1.

The forward end of the piston 33 has a close sliding fit with the blind forward end of the central bore in the hammer member 31 providing an expansible chamber 45. A nipple 51 having an axial bore therethrough' has its rearward end tightly secured in the forward end of the drive shaft 16 so that air under pressure from the supply of motive fluid may pass through the bore in the drive shaft 16 and through the central bore in the nipple 51. The forward end of the nipple 51 fits slidably in a bore 52 in the rear end of the piston 33 forming an expansible chamber 54 substantially smaller in diameter than the chamber 45 at the forward end of the piston 33. A small bore 37 connects the chamber 54 with the cross bore 34a in which the valve 35 is slidably mounted. Preferably, a seal 39 surrounds the forward end of the nipple 51 to prevent leakage from the chamber 54.

The valve 35 is formed with an annular groove 38 in constant communication with the small bore 37. A bore 44 extends axially through the forward end of the piston 33 between the expansiblechamber 45 and the cross bore 34a. When the valve 35 is in its outward position as illustrated in full lines in Fig. l, the inner end of the valve 35 clears the bore 44 so that the chamber 45 is open to atmosphere through the bores 44, 34a and communicating bores 43 and 43a formed in and extending to the end of the impact pin 32. When the valve 35 is in its inner position as indicated in dotted lines in Fig. 1, its inner end closes the bore 44 from exhaust and the annular groove 38 connects the bore 37 with the bore 44 so that high pressure air enters the expansible chamber 45. r

The valve 35 is constantly urged to its inward position by air pressure. For this purpose a blind bore 55 extends axially into the valve 35 from the outer weighted end 36 and communicates with a cross bore 56 opening into the annular groove 38. A pin 57 slidably fits in the bore 55 and slidably engages the wall of the recess in the hamrner member 31 which accommodates the enlarged head 36 of the valve. Thus live air pressure entering the groove 38 and the bores 55 and 56 acts against the blind inner end of the bore 55 and against the inner end of the pin 57 so as to urge the valve 35 inwardly.

When the valve 35 is in its outer position the expansible chamber 45 is open to atmosphere and live air pres sure in the smaller chamber 54 urges the piston 33 forwardly, thus tending to move the impact pin 32 into the path of the anvil surfaces 33. The valve 35 is moved into and held in this outer position by centrifugal force overcoming the air pressure acting upon the bore 55 and pin 57. When the centrifugal force is insufficient to overcome the force produced by the air the valve 35 moves to its inner position so that the chamber 45 is cut off from exhaust and open to live air through the annular groove 38 and the bore 44. Air pressure acting on the greater diameter of the chamber 45 overcomes the force of the air in the chamber 54 and moves the piston 33 quickly and positively to its rearward position as shown in Fig. 1 so that the impact pin 32 is pulled out of the path of the anvil surfaces 30 and the motor torque accelerates the hammer 31 for the next blow.

In the disclosed embodiment, acceleration of the hammcr through more than one complete revolution is achieved by means of a latch 46 pivotally mounted on a pin 58 and disposed in a recess 59 in the wall of the hammer 31 between the rearward end of the output shaft 26 and the impact pin 32. A spring 47 wrapped around the pivot pin 58 having a bight engaging the latch 46 and free ends engaging an anchor pin 60 urges the latch 46 to pivot in a counter-clockwise direction as seen in Fig. 1. A notch 48 formed in the impact pin 32 is arranged to receive the rearward end of the latch 46 when the impact 32 is in its retracted position as shown in Fig. l, in which position the latch acts to prevent forward movement of the impact pin 32 into the path of the shoulders 3d.

The rearward end of the output shaft 26 is formed with a cam 49 disposed rearwardly of and in line with the center of the anvil 29. The cam 49 is positioned to engage the forward end of the latch 46 and has a lift sulficient to rock the latch 46 about the pivot pin 58 to withdraw its rearward end from the notch 48 and thereby free the impact pin 32 for forward movement. The portions of the cam in which the lift is sufiiciently high to release the latch 46 are preferably confined to the central portion of the anvil 29, so that when the pin 32 is released his in axial alignment with the surface 61.

When the impact pin 32 strikes one of the impact surfaces 39 the parts are in the position shown in Figs. 3 and 4. As soon as the hammer has delivered all, or substantially all, of its momentum to the anvil 29 the unbalanced air pressure acting on the valve 35 moves the valve 35 inwardly so as to admit live air to the cxpansible chamber 45 and retract the impact pin 32 so that it can pass over the anvil 29. When the impact pin 32 reaches its rearward position the latch 46 is pressed by the spring 47 into the notch 48. As the hammer 31 and the impact pin 32 and latch 46, carried thereby, start to rotate under the motor torque so as to move the impact pin 32 over the anvil 29, the cam 49 engages the outer end of the latch 46 and moves it into released position. This, however, occurs at the very beginning of the acceleration of the hammer after it has delivered an impact blow, so that the latch 46 moves completely past the cam 49,

, allowing the rearward end of the latch to again drop 45 until the latch 46 has been moved past the cam 49 and has returned to latching position, on the first passage of the latch past the cam 49 after a blow has been struck and the pin has been retracted.

Before the hammer has been accelerated through one revolution, centrifugal force has thrown the valve 35 to its outward position exhausting the air from the chamber 45 so that the live air pressure in the chamber 54 acts to move the pin 32 into impacting position. Such forward movement of the impact pin 32 is prevented by the latch 46 until after the pin 32 has passed the impact surface 30 towards which it is rotating and the outer end of the impact pin 32 is over the anvil 29. At this time the cam 49 withdraws the latch 46 from the notch 48 and the air pressure in the expansible chamber 54 immediately forces the impact pin 32 forwardly into contact with the flat rearward surface 61 of the anvil 29, thereby moving the notch 48 out of alignment with the latch 46, as shown in Fig. 6. Since the pin 32 has already passed the impact surface 30 when the latch is released, no impacting occurs and free acceleration of the hammer under the motor torque continues for another revolution. As soon as the forward end of the impact pin 32 slides off the anvil 29, the pin continues its forward movement under the force of the air pres sure in the chamber 54 into alignment with the impact shoulders 30, so that at the end of the second revolution another impact blow is delivered to the anvil 29.

The latch 46 and cam 49 operate in the same manner to permit acceleration of the hammer through two complete revolutions between impact blows no matter in which direction the hammer assembly is rotated, because the high point of the cam 49 which etfects release of the latch 46 is located in line with the center of the anvil.

In the embodiment disclosed the weighted valve 35 moves radially within the hammer 31 to effect a rapid snap action of the valve in each direction. Thus, in the inner position of the valve the mass and effective radius of the weighted end 36 determine the angular velocity required to produce centrifugal force of sufficient magnitude to overcome the unbalanced air pressure tending to hold the valve in its inner position. As soon as this velocity is reached the valve starts to move outwardly, thereby increasing the effective radius of the mass 36 and increasing the centrifugal force, so that once started the valve moves very quickly to its outer position. Likewise, when the valve is in its outer position, in order to reduce the centrifugal force to a small enough value to be overcome by the unbalanced air pressure acting on the valve it is necessary to slow the hammer assembly to a lower velocity than that which was required to initiate outward movement of the valve. Once the inward movement of the valve starts, the effective radius of the mass 36 decreases reducing the centrifugal force so that the valve snaps inwardly very quickly.

With this arrangement it is found that the relation between the unbalanced air pressure acting on the valve and the mass and effective radius of the weighted end 36, which insures both full impacting each revolution and positive disengagement after each blow in the absence of the latch 46, is also a satisfactory relation to insure acceleration through two full revolutions after each impact blow when the latch 46 is employed. It will be understood, however, that both the retention of the latch 46 in the notch 48 the first time the latch passes the cam 49 after an impact blow, and the forward movement of the pin 32 to move the notch 48 out of line with the latch 46 the second time the latch passes the cam 49, may be assured by adjustment of the relation between the unbalanced air pressure acting on the valve 35 and the mass and effective radius of the weighted end 36, as by varying the size of the bore 55 to vary the unbalanced air pressure on the valve, or by varying the size or radius of the weight 36.

' When the tool disclosed is used for running down and tightening a nut the output shaft and the nut are initially rotated at the same speed as the hammer, the impact pin 32 remaining in is forward position in engagement with an anvil surface 30, until the resistance of the work is sufiicient to overcome the motor torque and slow the rotation. As the speed of rotation approaches zero the valve 35 snaps inwardly, admitting air pressure to the chamber 45 and positively pulling the pin 32 out of engagement with the anvil surface 30. The full motor torque then acts to accelerate the hammer 31 and after the latch 46 has passed the high point of the cam 49 the first time the valve 35 snaps to its outward position so that the pin 32 is urged forwardly by the air pressure in the chamber 54, but is restrained from moving by the latch 46. As soon as the latch 46 again passes the high point of the cam 49 the air pressure moves the pin 32 forwardly to move the notch 48 out of latch-engaging position, and at the end of the next revolution the pin 32 strikes the impact surface 3%). Substantial stalling or rebounding of the hammer as a result of the impact blow again reverses the valve and retracts the pin32 for acceleration through two more revolutions.

It will be apparent that the elapsed time between blows is increased but slightly since the time required for acceleration through the second revolution is much less than that required for the first. Nevertheless, the momentum delivered by the hammer is increased substantially since this momentum increases with the square of the attained velocity. Thus with the present invention a tool of a given size can produce substantially greater impact torques, or a tool for delivering a given torque can be made much smaller, lighter, and cheaper, without substantial or objectionable increase in the elapsed time between blows.

Although the foregoing description is necessarily of a detailed character,-in order that the invention may be completely set forth, it is to be understood that the specific terminology is not intended to be restrictive or confining, and that various rearrangements of parts and modifications of detail may be resorted to without departing from the scope or spirit of the invention as herein claimed.

I claim:

1. A rotary impact tool comprising, a driving motor, a rotatable anvil, a rotatable impact element driven by said motor for driving said anvil, actuating means for moving said element into position to strike said anvil, means for moving said element out of anvil striking position, latch means for automatically locking said element out of striking position each time said element is moved out of its anvil striking position, and cam means fixed to said anvil for releasing said element from its locked position after rotation of said element with respect to said anvil through a predetermined angular extent.

2. In a rotary impact tool comprising, a driving motor, a rotatable anvil member, a rotatable hammer member driven by said motor for driving said anvil member, each of said members including a part having an impact surface adapted to engage an'impact surface on the other member, means for moving one of said parts out of engaging position to permit said hammer member to be rotated by said driving motor without rotating said anvil member, and means for yieldably urging said one part into engaging position, the improvement comprising latch means secured to one of said members for latching said one part out of engaging position and cam means carried by the other of said members for releasing said latch means after rotation of said hammer member relative to said anvil member through a predetermined angular extent.

3. A rotary impact tool comprising, a driving motor, a rotatable work shaft, a rotatable anvil, a rotatable impact driving element driven by said motor for driving said anvil, actuating means for exerting bias force for moving said element into position to strike said anvil when said element is rotated at a predetermined speed, means for moving said element out of engagement with said anvil when the rotation of said element drops below a predetermined lower speed, latch means for automatically locking said element out of striking position each time said element is moved out of engagement with said anvil, and a cam connected to said anvil adapted to release said latch means after rotation of said element with respect to said anvil through a predetermined angular extent.

4. A rotary impact tool comprising, a reversible motor, a rotatable impact delivering element driven by said motor, a rotatable anvil having oppositely facing impact receiving surfaces adapted to be struck by said element for rotating said anvil in either direction, said element being movable into a striking position in which its rotary path intersects said impact receiving. surfaces, and into a retracted position in which its path is spaced from said impact receivin surfaces, means for moving said element into its retracted position after said element has deivered an impact blow to said anvil, means for yieldably urging said element into its striking poistion, a latch for latching said element in its retracted position, and a cam on said anvil for releasing said latch when said element is aligned with said anvil and between said impact receiving surfaces.

5. In an impact wrench, a hammer element comprising a rotatable mass, an impact pin slidably mounted in said hammer element with its axis substantially parallel with and spaced from the axis of rotation, said impact pin being mounted for axial sliding movement to a striking position and to a retracted position, and releasable latch means carried by said hammer element to latch said impact pin into retracted position.

6. In a rotary impact tool comprising a driving motor, a rotatable anvil, a rotatable impact delivering element driven by said motor for striking and driving said anvil, said element being movable into striking position and into retracted position, actuating means including fluid pressure actuated means and a centrifugally operated valve for moving said impact delivering element into striking position when said valve is rotating at a predetermined speed and bias means continually exerting a bias force on said valve in the direction opposite to the direction of centrifugal force on said valve for causing said actuating means to move said impact delivering element into retracted position when the rotation of said valve drops below a predetermined lower speed; the improve ment comprising means for locking said element in retracted position each time it is retracted, and means for permitting said element to be advanced to the anvil engaging position on each alternate revolution thereof.

7. In a rotary impact tool having a driving motor, a hammer connected to be rotated by said motor, a rotatable driven member coaxial with said hammer having an impact receiving surface, an impact element mounted on said hammer for movement into a position to strike said impact receiving surface and into a retracted position out of engagement with and spaced from said surface, fluid pressure means for yieldably urging said element alternately into striking poistion and into retracted position, latch means for holding said element in retracted position, and a cam on said driven member for releasing said latch means after said element has rotated past said surface.

8. A rotary impact tool comprising, a driving motor, a rotatable anvil member, a rotatable hammer member driven by said motor for driving said anvil member, each of said members including a part having an impact surface adapted to engage an impact surface on the other member, said impact surfaces being substantially parallel to the axis of rotation of said anvil member, separate means for moving one of said parts out of engaging position to permit said hammer member to be rotated by said driving motor without rotating said anvil memher, and means for moving said one part into engaging position operable only after said hammer member has completed more than one complete revolution relative to said anvil member.

9. -In an impact wrench, a hammer element comprising a rotatable mass, an impact element movably mounted thereon for movement to a striking position and to a retracted position, said element being eccentric to and positioned to be revolved about the axis of rotation when said hammer element is rotated, said impact element having a shoulder thereon extending transversely to its direction of movement into striking position, and releasable latch mews carried by said hammer element and engageable with said shoulder to latch said impact element in retracted position.

References Cited in the file of this patent UNITED STATES PATENTS 2,338,358 Schmied Jan. 4, 1944 2,373,664 Emery Apr. 17, 1945 2,693,867 Maurer u Nov. 9, 1954 2,801,718 Kaman Aug. 6, 1957 FOREIGN PATENTS 700,706 Great Britain Dec. 9, 1953 

